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VUCOMISH

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Henk-Jan Lebbink edited this page Jun 4, 2026 · 1 revision

VUCOMISH — Unordered Compare Scalar FP16 Values and Set EFLAGS

Opcode/ Instruction Op/ En 64/32 bit Mode Support CPUID Feature Flag Description
EVEX.LLIG.NP.MAP5.W0 2E /r VUCOMISH xmm1, xmm2/m16 {sae} A V/V AVX512_FP16 OR AVX10.1 Compare low FP16 values in xmm1 and xmm2/m16 and set the EFLAGS flags accordingly.

Instruction Operand Encoding

Op/En Tuple Operand 1 Operand 2 Operand 3 Operand 4
A Scalar ModRM:reg (w) ModRM:r/m (r) N/A N/A

Description

This instruction compares the FP16 values in the low word of operand 1 (first operand) and operand 2 (second operand), and sets the ZF, PF, and CF flags in the EFLAGS register according to the result (unordered, greater than, less than, or equal). The OF, SF and AF flags in the EFLAGS register are set to 0. The unordered result is returned if either source operand is a NaN (QNaN or SNaN).

Operand 1 is an XMM register; operand 2 can be an XMM register or a 16-bit memory location.

The VUCOMISH instruction differs from the VCOMISH instruction in that it signals a SIMD floating-point invalid operation exception (#I) only if a source operand is an SNaN. The COMISS instruction signals an invalid numeric exception when a source operand is either a QNaN or SNaN.

The EFLAGS register is not updated if an unmasked SIMD floating-point exception is generated. EVEX.vvvv are reserved and must be 1111b, otherwise instructions will #UD.

Operation

VUCOMISH

RESULT ← UnorderedCompare(SRC1.fp16[0],SRC2.fp16[0])
if RESULT is UNORDERED:
    ZF, PF, CF ← 1, 1, 1
else if RESULT is GREATER_THAN:
    ZF, PF, CF ← 0, 0, 0
else if RESULT is LESS_THAN:
    ZF, PF, CF ← 0, 0, 1
else: // RESULT is EQUALS
    ZF, PF, CF ← 1, 0, 0
OF, AF, SF ← 0, 0, 0

Intel C/C++ Compiler Intrinsic Equivalent

VUCOMISH int _mm_ucomieq_sh (__m128h a, __m128h b);
VUCOMISH int _mm_ucomige_sh (__m128h a, __m128h b);
VUCOMISH int _mm_ucomigt_sh (__m128h a, __m128h b);
VUCOMISH int _mm_ucomile_sh (__m128h a, __m128h b);
VUCOMISH int _mm_ucomilt_sh (__m128h a, __m128h b);
VUCOMISH int _mm_ucomineq_sh (__m128h a, __m128h b);

SIMD Floating-Point Exceptions

Invalid, Denormal.

Other Exceptions

Source: Intel® 64 and IA-32 Architectures Software Developer's Manual, Combined Volumes (Order Number 325462-091US, March 2026)
Generated: 7-6-2026

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